The dyeing of shaped articles, especially garments of a synthetic material such as polyester, is carried out with a dyestuff dispersed in an aqueous bath. The textile material is placed in the bath for a long enough time period to allow sufficient dyestuff to be absorbed to provide the desired coloration.
Such a dyeing process poses several disadvantages and limitations. Since the temperature of the aqueous bath cannot exceed the boiling temperature of the water, the process cannot be conducted at elevated temperatures, unless high pressure is used. Even then temperatures of only 250.degree. F. to 270.degree. F. are reached. Consequently, relatively long dyeing cycles are needed.
Additionally, the aqueous bath is generally disposed of after each dyeing cycle because most of the dyestuff has been absorbed by the textile material. The disposal of the used dye bath presents obvious environmental problems, as well as economic losses due to discharge of the residual dyestuff and chemicals remaining in the bath.
Dyeing at elevated temperatures with a non-aqueous system overcomes many of these problems and provides several advantages. Elevated temperatures reduce the time needed to dye the textile material. Shorter dyeing cycles make the process more economical and efficient.
Various dye processes that use non-aqueous dye compositions have been proposed for the treatment of textile materials. One technique involves immersing the textile material in a bath comprising an organic dyestuff dissolved in a high boiling aromatic ester or a cycloaliphatic diester. Such dyeing processes have several inherent disadvantages that prevent their effective and efficient use. The dye composition does not remain stable over a period of time when used in an ambient atmosphere; significant degradation of the dye composition often occurs after only a few hours of use.
Whether the dye composition is aqueous or non-aqueous, it is usually brought into contact with the textile material by spraying or showering, or by immersion. Spraying or showering is basically a pressurized operation in which the dye composition is applied to the textile material in the form of droplets. Examples of spraying or showering processes are provided in U.S. Pat. Nos. 3,868,835 to Todd-Reeve, 3,557,395 to Kronsbein, 3,181,750 to Helliwell et al., and 3,131,840 to Berger et al.
Spraying or showering techniques have several limitations and disadvantages. Since the dye composition cools as it is sprayed or showered through the air, the dye composition cannot be maintained at a constant temperature. Such temperature fluctuations result in poor dye uniformity, especially at elevated temperatures, such as 350.degree. F. to 380.degree. F.
Since it is difficult to maintain the dye composition at an elevated temperature during the spraying or showering, longer periods of time are needed for complete dyeing to occur. If the dye cycle is shortened, uniform dyeing will not be achieved and a relatively poor quality product results. Also, spraying or showering exposes the largest surface area of the dye composition to the atmosphere.
Immersion techniques are disadvantageous, since large volumes of the dye composition are needed. Even though immersion provides better heat transfer than spraying or showering, such processes are inefficient and uneconomical.
In short, present apparatus and processes are incapable of dyeing uniformly a shaped article with a non-aqueous dye composition in a sufficiently short time period at an elevated temperature and with a minimal amount of dye composition. This is particularly true with respect to some synthetic materials, such as polyester, that are difficult to dye.